Conventionally, a method in which an iron compound that is used as an oxygen absorber is dispersed in resin to be allowed to exhibit its function has been known as a method of absorbing oxygen (for instance, JP2002-249174A). There, however, has been a problem that since, for instance, iron oxide is used as an oxygen absorber, the oxygen absorber dissolves in water to elute. Furthermore, one molecule of iron compound absorbs only one molecule of oxygen. Accordingly, in order to absorb a sufficiently large amount of oxygen, a large amount of iron compound is necessary.
Furthermore, an oxygen-absorbing material also has been known that includes a transition metal compound (a catalyst) and an oxidizable polymer. For instance, a composition has been disclosed that is obtained by adding 10 to 100000 ppm of transition metal compound expressed in terms of metal, such as cobalt, iron, manganese, etc., to polyamide containing at least 40 mol % of m-xylylene adipamido (MXD6 nylon) (JP2002-241610A).
JP5(1993)-115776A discloses a composition containing ethylenically unsaturated hydrocarbon such as polybutadiene, polyisoprene, a styrene-butadiene copolymer, carotenoid, etc. and a transition metal compound such as cobalt, manganese, iron, nickel, copper, etc.
The PCT pamphlet of WO01/90238 discloses a composition that contains a polymer having an unsaturated bond, a transition metal compound, and a polymer having an oxygen barrier property, for the purpose of obtaining a composition having both the oxygen barrier property and an oxygen scavenging property.
Moreover, JP5(1993)-156095A discloses a resin composition with an oxygen barrier property. This composition is obtained by dispersing an oxygen-absorbing composition containing a polyolefin such as polyethylene, polypropylene, an ethylene-alpha olefin (with at least three carbon atoms) copolymer, etc. and an oxidation catalyst made of a compound of transition metal such as cobalt, manganese, iron, copper, nickel, etc., in a saponified ethylene-vinyl acetate copolymer.
In the case of a conventional oxygen-absorbing material containing an oxidizable polymer and a transition metal compound, oxygen contained in the air is absorbed when the polymer is oxidized. In this case, the transition metal compound has an effect of promoting the oxidation of the polymer. Hence, in order to allow the oxygen-absorbing material to exhibit sufficiently high oxygen absorbency, a certain amount of transition metal compound is required. However, when it is used as a packaging material for goods such as food, drink, medical supplies, cosmetics, etc., it is desirable to limit the amount of the transition metal compound to be used, in consideration of the safety. Accordingly, with the conventional oxygen-absorbing material containing a transition metal compound and an oxidizable polymer as essential constituent elements, it is not easy to meet such contradictory conditions and thereby to obtain a material that can satisfy both the safety and the oxygen absorbency.
On the other hand, methods have been disclosed in which various alkanes, alkenes, and various high molecular compounds are oxidized using an N-hydroxyphthalimide that serves as an oxidation catalyst. For instance, it has been disclosed that an N-hydroxyimide compound that coexists with various metal salts reacts with oxygen contained in the air to serve as an oxidation catalyst for alkane, alkene, and alcohol (Chemistry Vol. 56, No. 7, 18-23 (2001) and Journal of Synthetic Organic Chemistry, Vol. 59, No. 1, 4-12 (2001)).
Furthermore, a method has been disclosed in which various polymers are denatured with gas containing oxygen atoms using an N-hydroxyimide compound as a catalyst (JP2000-290312A). It is described that this method allows a polar group to be introduced efficiently into a polymer without cutting the main chain of the polymer and as a result, a polymer can be obtained that is excellent in antistatic property, etc.
These oxidation reactions, however, are allowed to occur in the presence of a polar solvent such as acetic acid, etc., i.e. in the presence of a solvent that absorbs oxygen actively. These reactions are oxidation reactions that occur between a liquid phase and a liquid phase or between a solid phase and a liquid phase and therefore are predicated on the intervention of transition metal and the flow of a catalyst that occurs in the liquid. On the other hand, it is required that the oxygen-absorbing material maintains its solid state even when it absorbs oxygen. Accordingly, the reaction that is required to take place in the oxygen-absorbing material is the reaction that occurs between the solid phase and the vapor phase. However, possibilities of the occurrence of such a reaction have not been studied at all.